1. Field of the Invention
The present invention relates to a motor, and more particularly to a motor having a rotor which combines a permanent magnet type rotor unit and a reluctance type rotor unit for the sake of enhanced flexibility in design.
2. Description of Related Art
Conventionally, there have been motors in which a permanent magnet type rotor unit having a plurality of permanent magnets and a reluctance type rotor unit having a plurality of salient pole portions are coupled to each other in the axial direction for the sake of enhanced flexibility in design. The known examples include ones disclosed in Japanese Patent Laid-Open Publications Nos. Hei. 7-59310 and Hei. 9-294362.
Japanese Patent Laid-Open Publication No. Hei. 7-59310 discloses that the permanent magnets and the salient pole portions are given an angle deviation therebetween in the direction of rotation to obtain desired characteristics, and that a nonmagnetic material is interposed into the stator and between opposed portions of the permanent magnet type rotor unit and the reluctance type rotor unit of the rotor so that flux leakage from the permanent magnets to the reluctance type rotor unit is prevented to avoid coupling in terms of magnetic circuits.
In Japanese Patent Laid-Open Publication No. Hei. 9-294362, however, the permanent magnet type rotor unit and the reluctance type unit are simply combined with each other. This causes a problem of inevitable deterioration in characteristics due to interactions. More specifically, the problem is that the magnetic flux from the permanent magnets of the permanent magnet type rotor unit can leak out to the reluctance type rotor unit, ending up with deterioration in characteristics. Moreover, since a current phase value at which the permanent magnet type rotor unit generates a maximum torque is different from one at which the reluctance type rotor unit generates a maximum torque, there is the problem that the combined torque does not reach the sum of the maximum values.
Meanwhile, in Japanese Patent Laid-Open Publication No. Hei. 7-59310, the interposition of the nonmagnetic material between the permanent magnet type rotor unit and the reluctance type rotor unit prevents the flux leakage, whereas there are problems of greater size and higher cost.
Among possible technical means for solving these problems is one disclosed in Japanese Patent Laid-Open Publication No. Hei. 11-196544 in which the reluctance type rotor unit is provided with slits for interrupting magnetic flux from the permanent magnets. Now, an example of such configuration will be described with reference to FIGS. 16A–16C. The reference numeral 1 represents a motor, which includes a rotor 2 and a stator 3. The rotor 2 includes a permanent magnet type rotor unit 4 having 2n (n is a natural number) permanent magnets 5 and a reluctance type rotor unit 6 having a plurality of salient pole portions 7. The rotor units 4 and 6 are coupled to each other in the axial direction. The reluctance type rotor unit 6 has slits 8 for preventing flux leakage from the ends of the permanent magnets 5. The slits 8 are formed symmetrically about the center of the salient pole portions 7 so as to run within projected sections of the permanent magnets 5. The stator 3 is provided with 3n teeth 9. Each of the teeth 9 is given a winding 10 so as to generate a magnetic field for driving the rotor 2.
Practical experiments showed, however, that even in such configuration, i.e., when the slits 8 were formed to fall within the projected sections of the permanent magnets 5, flux leakage through outside the ends of the slits 8 was considerably greater than expectations. That is, the flux leakage from the ends of the permanent magnets 5 to the reluctance type rotor unit 6 could not be prevented satisfactorily.
Besides, if the permanent magnet type rotor unit 4 and the reluctance type rotor unit 6 are coupled to each other in the axial direction with an angle deviation in the direction of rotation so that the combined characteristics of the torques generated by the permanent magnet type rotor unit 4 and the reluctance type rotor unit 6 become desirable, there may occur the problem that the effect of the slits 8 is insufficient.